Method for the plasma-ac remelting of a consumable metal bar in a controlled atmosphere

ABSTRACT

A method for plasma-arc remelting of a material under a controlled atmosphere consists in making the material to be remelted in the form of a consumable hollow electrode-bar and electrically melting down the hollow electrode-bar so formed, in a cooled mold before finally stripping the remelted ingot off the mold. The method also includes generating a low temperature plasma at a tip of the consumable electrode which is connected to a power source, by supplying plasma-generating gas into an arcregion, through the hollow of the consumable electrode bar. Stabilizing the plasma-arc during operation without giving rise to transient arc plasma is expediently achieved by feeding preselected amounts of flux into the arc-region, thereby producing an ingot free from flaws and impurities.

United States Patent 1 91 Paton et a].

[ 1 Mar. 27, 1973 METHOD FOR THE PLASMA-AC REMELTING OF A CONSUMABLEMETAL BAR IN A CONTROLLED ATMOSPHERE menko, ulitsa Sovetskaya, 21, kv.-

l7, Izhevsk, all of U.S.S.R.

22 Filed: June 28, 1971 21 Appl. No.: 157,262

52 US. (:1. ..13/1, 13/9, 13/18 51 1.1.121. ..H05b 7/00, HOSb 7/18 [58]FieldotSem-ch 1.13/9, 1, 31, 18; 219/121 P [56] References Cited UNITEDSTATES PATENTS 3,105,864 10/ l 963 Robinson 1 3/9 3,496,280 2/1970Dukelow et a1" ..2l9/ 1 2| P X Primary Examiner--Roy N. Envall, Jr.Attorney-Holman & Stern ABSTRACT A method for plasma-arc remelting of amaterial under a controlled atmosphere consists in making the materialto be remelted in the form of a consumable hollow electrode-bar andelectrically melting down the hollow electrode-bar so formed, in acooled mold before finally stripping the remelted ingot off the mold.The method also includes generating a low temperature plasma at a tip ofthe consumable electrode which is connected to a power source, bysupplying plasma-generating gas into'an arcregion, through the hollow ofthe consumable electrode bar. Stabilizing the plasmafarc duringoperation without giving rise to transient arc plasma is expedientlyachieved by feeding preselected amounts of flux into the arc-region,

thereby producing an ingot free from flaws and impurities.

2 Claims, 1 Drawing Figure METHOD FOR THE PLASMA-AC REMELTING OF ACONSUMABLE METAL BAR IN A CONTROLLED ATMOSPHERE BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates toelectrical metallurgy and is directed to the production of ingots ofclean metals, high-quality steels and alloys in electric furw naces.

2. Description of the Prior Art Hitherto, the most commonly used methodfor that purpose has been the method of vacuum arc remelting. With theabove process a free-burning electric arc is used as a source of heatand melt the metal which is protected from any harmful effect ofatmosphere by using vacuum.

However, inherent in the foregoing method is a series of drawbacks.Thus, in remelting the alloys comprising the alloying constituents suchas manganese characterized by a high vapor pressure, they tend tovolatilize with ensuing deterioration in the alloy composition. Besides,by using the above technique treatment of the liquid metal with gasesor/and fluxes is impracticable.

Known in the prior art is also a procedure for the plasma-arc remeltingof metal which is in the form of a consumable metallic bar undercontrolled atmosphere conditions in which an ingot is formed in a cooledmould connected to a power source (see FRG Patent application No. P. 1758 483.7).

With this production method a direct-acting arc plasmatron acts as heatsource and transmission of heat to the metal is effected mostly by astream of hot gas with the plasma arc. zone located above the mouldwhich is equipped with the ingot stripping gear.

By using the foregoing procedure the occurence of selective vaporizationof the alloying elements can be avoided by controlling the workingpressure in a melting chamber. Furthermore, the possibility of employingvarious gas media allows the metallurgical reactions to be controlled.

Yet, this method also is associated with of shortcomings.

The plasmatrons, provided by the aforesaid technique, are intricate indesign and are expensive. Moreover, characteristic of them is loweffective thermal efficiency by virtue of which they require very largeamounts of gas for operation.

Since with the above procedure the arc zone is located above the mouldthis results, on the one hand, in heavy losses of heat due to radiationrequired for heating the walls of the furnace melting chamber and, onthe other hand, in a need for a high priced and intricate mould fittedwith the ingot stripping gear.

SUMMARY OF THE INVENTION It is an object of the present invention todevelop a method for the plasma-arc of a metal or an alloy in the formof a consumable bar under controlled atmosphere power supply. Accordingto the present invention, a hollow bar is manufactured and placed in themould whereupon between the face of the bar, through which an electriccurrent flows, and a metal bath a low-temperature (arc) plasma isgenerated by feeding the plasma-generating gas through the hollow barwith the plasma arc zone being gradually shifted upwards as the bar isbeing flashed off.

As an additional means to further improve the stability of an arcplasma, it would be expedient to feed flux in the plasma arc zone.

As a result of the present invention a method has been established forthe plasma-arc remelting of a consumable metal bar under controlledatmosphere conditions which would make it possible to simplify theconstruction of a plasma-arc furnace, ensure a substantial reduction inits cost, increase the furnace efficiency and reduce the consumption ofthe plasma-generating gas.

BRIEF DESCRIPTION OF DRAWING To make the present invention more cleargiven below is an exemplary embodiment and the drawing which is adiagrammatic representation of the furnace (in longitudinal section) forcarrying into' production the plasma-arc remelting method in conformityto the present invention.

DESCRIPTION OF EMBODIMENT Placed inside of solid-bottom copper cooledmould 4, coaxially with it, is consumable metal bar 1 with internallongitudinal cavity 2 contained in the furnace chamber. Either a DC. orA.C. current is supplied to bar 1 and mould 4. The furnace chamber 3, onbeing initially evacuated, is then filled up with a plasmageneratinggas. In mould 4, interior between the lower face of bar 1 and liquidmetal bath 5 plasma is conditions which would enable a more simpleconstrucgenerated. Besides, passed through cavity 2 in bar 1 is theplasma-generating gas which may be either inert or active with respectto the metal being remelted, and the gas may be argon, gelium, nitrogenor hydrogen.

Low-temperature (arc) plasma 6 is steadily generated between the lowerface of bar 1 and liquid metal bath 5.

Both the melting of bar I and maintaining liquid metal bath 5 iseffected owing to the heat generated in the arc regions adjacent toelectrodes, radiation of the arc column and a stream of hot gas.

As bar 1 is being flashed off, the arcing zone of arc plasma'6 isdisplaced upwards, the rate of this travel being controlled by changingthe speed at which bar 1 is fed.

Control of the gas atmosphere can be accomplished by varying both thecomposition of a plasma-generating gas and the pressure values in thefurnace chamber 3.

In order to facilitate ionization of the gas contained in the spacebetween the lower face of bar 1 and metal bath 5,'eliminating therebythe possibility of generating transient arc plasma, i.e., in order tomake the plasma more stable, flux 7 is fed onto the surface of metalbath 5 containing readily ionizing substances and this forms a slag. Atthe same time the flux 7 is intended for refining the metal. lngot 8 isformed in mould 4 titted with a solid bottom.

The proposed procedure'has been employed efficiently for remelting steelbars in a water-cooled copper mould. The remelting process has beeneffected by operating on both a D.C. and AC. currents in the atmospheremade up of argon and nitrogen or of a mixture of argon with eithernitrogen or hydrogen and with flux fed on the metal bath.

The trial heats have proved high stability of arc plasma. Besides,consumption of a plasma-generating gas has been reduced by some 20-25percent and power input by to percent compared to the conventionaltechnique of plasma-arc remelting.

When compared with the vacuum arc remelting process, power input hasbeen decreased by to percent.

The surface of the ingots fabricated has been smooth, blow holes havebeen absent.

We claim:

1. A method for plasma-arc remelting of a metal or alloy which is in theform of a consumable bar, under controlled atmospheric conditions,comprising: making said metal or alloy in the form of a hollowconsumable bar; movably setting up the hollow bar to dip in a cooledmould in which an ingot of the material of the Y consumable bar is to beformed; connecting an electrical power supply source between said hollowmetal bar and the mould body so as to flash an arc therebetween;delivering a plasma'generating gas through the hollow bar into a spaceat the end of the bar which dips into the mould so as to generate insaid space a low temperature plasma; and shifting of the plasma-arc-zoneupwards as the barmelts down and is slowly consumed to shape thematerial of the hollow bar into the mold.

2. A method as claimed in claim 1 which includes the steps of feedingplasma flux material into the plasma arc zone and eliminating formationof transient arc plasma in order to stabilize the arc in said spaceatsaid end of the bar.

1. A method for plasma-arc remelting of a metal or alloy which is in theform of a consumable bar, under controlled atmospheric conditions,comprising: making said metal or alloy in the form of a hollowconsumable bar; movably setting up the hollow bar to dip in a cooledmould in which an ingot of the material of the consumable bar is to beformed; connecting an electrical power supply source between said hollowmetal bar and the mould body so as to flash an arc therebetween;delivering a plasma-generating gas through the hollow bar into a spaceat the end of the bar which dips into the mould so as to generate insaid space a low temperature plasma; and shifting of the plasma-arc-zoneupwards as the bar melts down and is slowly consumed to shape thematerial of the hollow bar into the mold.
 2. A method as claimed inclaim 1 which includes the steps of feeding plasma flux material intothe plasma arc zone and eliminating formation of transient arc plasma inorder to stabilize the arc in said space at said end of the bar.